Cholestyramine of a crosslinked type, which is a conventional cholesterol depressant, is problematic in that its amount to be administered is large (8 to 16 g/day) and that it must be administered in the form of its suspension. Therefore, many studies have heretofore been made to produce tablets and coated tablets of anion exchange resins. For example, a method has been reported of coating tablets of a solid cholestyramine resin having a water content of from 8 to 14% with a melt of polyethylene glycol and stearic acid in the presence of no solvent to give coated tablets, which do not swell in the mouth (see Japanese Patent Application Laid-Open No. 3-236326).
Regarding tablets of an imidazole-type anion exchange resin (see Japanese Patent Application Laid-Open No.60-209523), known are a method of producing those tablets in the presence of a predetermined amount of water (see Japanese Patent Application Laid-Open No. 2-286621); a method of producing coated tablets by coating those tablets as prepared in the presence of a predetermined amount of water, with hydroxypropyl cellulose or the like (see Japanese Patent Application No. 4-320155 (published before examination as Laid-Open No. 6-157325)); and a method of producing those tablets in the presence of a predetermined amount of water and silicon dioxide (see Japanese Patent Application Laid-Open No. 7-97330).
However, the conventional methods require the addition of a predetermined amount of water to the hygroscopic anion exchange resins being tabletted.
The present inventors have already reported that non-crosslinked anion exchange resin represented by the formula (I): ##STR3## (wherein R.sub.1 is an aralkyl group having from 7 to 10 carbon atoms or An alkyl group having from 1 to 20 carbon atoms; R.sub.2 and R.sub.3 are each independently the same or different and represent a lower alkyl group having from 1 to 4 carbon atoms; R.sub.4 is a hydrogen atom or a lower alkyl group having 1-4 carbon atoms; X is a physiologically acceptable counter ion; n is an integer of from 1 to 3; and p is an average degree of polymerization of from 10 to 10,000) is extremely useful as a cholesterol depressant (WO 93/13781). Because this anion exchange resin is a non-crosslinked and linear polymer, it does not expand by swelling unlike cross-linked polymers such as cholestyramine and so on, so there is no side effects such as feeling of distension in the abdomen or constipation accompanying swelling. Further, the effective adsorption of bile acid per unit weight is large, so it is anion exchange resin of extremely high usefulness.
However, this agent is soluble in water and has strong astringency, and in addition, it is highly hygroscopic and deliquescent. Therefore, the novel, non-crosslinked cholesterol depressant comprising the compound of formula (II) is problematic in that, if tabletted in any of the conventional methods that require water in the mixing step, it is formed into tablets with poor strength and stability since its flowability and tablettability is very poor. Even if the cholesterol depressant comprising the compound of formula (II) is tabletted in the absence of water, the resulting tablets are still problematic in that they are very astringent because of the strong astringency intrinsic to the compound of formula (II) itself. The dose of the compound of formula (II), though varying depending on the case to which it is administered, is relatively large or is generally from 0.1 to 9 g/day, preferably from 0.1 to 5 g/day. Tablets comprising the compound of formula (II) and containing a large amount of vehicles in order to reduce the bitterness of the compound are problematic in that the number of the tablets to be administered at a time shall be large.
In order to produce practical medicine products comprising the compound of formula (II) with such extremely high usefulness, it is desired to formulate the compound into highly-stable preparations without strong astringent while adding thereto the smallest possible amount of vehicles as possible.